In recent years, ink jet printing technology has expanded from industrial labeling applications to office printing. These type of printers are low cost, near laser printing quality, low noise and maintenance, and have print speeds upwards of ten pages per minute for office applications. Another advantage of the use of ink jet printers is the development of consistent, high-quality color printing capabilities for the full range of colors. These attributes have made the ink jet printer one of the most popular office printers on the market today. More recently, ink jet printing technology has expanded into the reprographic market with the advent of large format ink jet plotters, such as the Hewlett Packard Designjet series and Encad's Novajet series. Generally, such plotters can produce a range of sizes of drawings and designs from the standard A size (8.5".times.11") up to an E size (36".times.48") plot. One example of the use of such ink jet plotters is the production of designs, floor plans, and structures by way of computer aided design (CAD) software. Architects and engineers are increasingly employing such CAD software for "drawing", thereby negating the need for the more conventional hand drafting techniques.
Ink jet printing technology is a form of printing that encompasses the projection of ink through a nozzle orifice, forming tiny droplets of a specific diameter, directly onto a substrate, such as paper or film, to form written symbols and drawn images. The ink jet printer receives electronic information, usually from application software via a computer, and converts the electronic information into legible hard copies. Several different technologies are used for such projection of ink droplets onto a substrate. For example, one technology utilizes a continuous stream of ink droplets being discharged from an ink reservoir through a nozzle. The droplets may then be deflected by means of an electrically charged field to the substrate. Those droplets not deflected to the substrate by the electrically charged field are allowed to flow in a straight stream and are collected and recirculated for reuse. Another example of ink jet printing technology is the use of heating elements for the direct stimulation of individual ink droplets. In this method of printing, the ink may be thermally excited by the heating element contact which causes the ink to be forced through the nozzle orifice and projected onto the substrate.
Ink compositions used in ink jet printing are carefully chosen by the manufacturer depending upon the technology used in the printer. Inks are usually manufactured to high quality standards to control the viscosity, particulate size, conductivity, surface tension, foaming, biological and chemical activity, lightfastness, and drying times. The inks must not be allowed to dry inside of the reservoir or in the nozzles of the printhead. To circumvent this problem, two types of ink jet inks have been developed: high boiling organic solvent and water combinations, and those that are essentially aqueous based. These solvent systems are vehicles for the ink dyes. In addition to the purified dyes, the inks may contain additives such as surface tension modifiers, pH buffers, defoamers, and fungicides, to make the ink acceptable for ink jet printing.
The use of aqueous and aqueous/high boiling organic solvent vehicles in ink jet printing creates the greatest challenge for the design of the media on which to print. These ink vehicles have slow evaporation rates to avoid drying or clogging of the inks in the nozzle or reservoir of the printer. However, the slow evaporation rate also impedes the drying of the ink on the surface of the substrate to which it is applied. Therefore, the inks can be smeared or rubbed off before they are completely dry. Also, low surface tensions of some inks can increase the lateral diffusion, or spreading, of the ink causing the images to be blurred. Control of the drying and absorption of the inks onto the surface of the recording media are of primary concern to the media design.
Great care must be taken in the design of recording media, whether paper, vellum, transparent or matted film, to provide a suitable means for recording ink jet printed symbols and images. In many cases, the base support used is inherently hydrophobic and thus repels the aqueous or aqueous/high boiling organic solvent based inks. Also, due to its hydrophobicity, the surface tension of the film is usually very high, therefore causing the inks to "bead" with a concomitant loss of edge acuity of the printed symbols and images. Due to these immediate problems, ink receiving media are often prepared by treating the surface of the base film with chemical coatings to alleviate the above mentioned problems.
In the art of producing matted, opaque coated films to be used as a printing substrate in ink jet printers or plotters, water soluble, hydrophilic natural and synthetic polymers may be used in combination with fillers, to provide the desired matte surface and opaque appearance to the film. Control of the lateral diffusion, or spreading, of the applied inks to matte type ink jet films and highly filled papers, however, is especially difficult. Forces such as capillary action, wettability of the filler, and surface tension of the ink used in the printing process contribute to the lateral spreading of the inks. Some amount of spreading is necessary to cause the blending of individual ink dots to give a more solid, uniform image appearance. However, excessive spreading leads to loss of image sharpness. Other desirable characteristics in a matte type ink receiving media include, enhanced image density, favorable visible and U.V. densities, anti-curling, long term stability of the printed image and of the media, high resistance to moisture degradation, and rapid drying times and resistance to smudging and fingerprinting. Yet another desirable characteristic in an ink receiving matte media is an optimal balance between hardness and porosity. Hardness is important for permitting pen or pencil writing, e.g. hand annotation of a printed image. If a coating is not sufficiently hard the pressure of such writing will damage the media, crushing or crumbling the coating layer and leaving impressions. However, hardness generally is inversely related to porosity, which is important for ink receiving and drying time attributes of the media.
A variety of matte ink receiving media have been developed. For example, U.S. Pat. No. 4,680,235 (Murakami et al.) describes the use of surface active agents in a surface recording layer which do not form a material insoluble in the ink composition in combination with a dye contained in the ink composition. The '235 patent further describes the use of white pigments, such as barium sulfate, calcium carbonate, silica, zinc oxide, titanium dioxide, and others, in combination with a binder and the surface active agent to create an opaque recording material for ink jet printers. U.S. Pat. No. 5,206,071 (Atherton et al.) discloses ink jet printing film media that comprise a transparent, translucent or opaque substrate having on at least one side thereof a water-insoluble, water-absorptive and ink-receptive matrix comprised of a hydrogel complex and a polymeric high molecular weight quaternary ammonium salt. The matrix may contain pigments and fillers to provide annotatability, rapid drying, image density and actinic transmissiveness. The matrix may also contain white pigments, such as titanium dioxide, to improve the image contrast to the matte films. Another example of matte ink jet film can be found in U.S. Pat. No. 4,732,786 (Patterson et al.), which discloses a coated ink jet printing substrate where the coating utilizes an insolubilized hydrophilic polymer. The coating contains a) from 0 to 90 parts by weight of pigment, b) from 0 to 95 parts by weight of binder, c) from 1 to 100 parts by weight of an insolubilized hydrophilic polymer, and d) from 0.1 to about 50 milliequivalents per gram of polymer of a polyvalent cation selected from metallic salts, complexes and partially alkylated metal compounds having a valence greater than one and a coordination number greater than two. Another example is disclosed in U.S. Pat. No. 5,023,129 (Morganti et al.) as an element useful for recording images using nonimpact type printing with a transparent support having an antistatic layer coated on one side and a print receptive layer coated on the other, or the print receptive layer may be coated over the antistatic layer. The print receptive layer is a combination of binder, crosslinking agent, whitener, and matte agent such as silica, rice starch, and methacrylate beads.
Notwithstanding these various matte ink receiving media, there remains a need for improved recording material with matte, opaque surfaces for receiving ink jet printed inks to produce high quality images with improved edge acuity, image enhancement, and an optimum balance between hardness and porosity. Additionally there is a need for an ink receiving media that has excellent archivability characteristics, resistance to fingerprinting and curling, and provides good reproducibility using conventional methods such as diazo reproductions and electrophotographic processes. Also, there is a need to improve over the prior art such properties as drying time of the printed inks, desirable visible density and U.V. density of the printed image, and moisture resistance of the coating.